Preparation of dimethyldecalins



United States Patent 3,346,656 PREPARATION OF DIMETHYLDECALINS Abraham Schneider, Los Angeles, Calif., assignor to Sun Oil Company, Philadelphia, Pa., a corporation of New Jersey No Drawing. Filed Jan. 10, 1963, Ser. No. 250,503 4 Claims. (Cl. 260-666) This application is a continuation-in-part of copending U.S. patent applications, Ser. Nos. 86,304 and 86,306, filed Feb. 1, 1961 both of which are now abandoned.

This invention relates to the preparation of dimethyldecalins by the catalytic dimerization of C naphthenes.

Dimethyldecalins other than those which have gem substitution can be dehydrogenated to form dimethylnaphthalenes. The latter can be partially oxidized to yield dibasic acids which can be utilized in the preparation of resins. While dimethyldecalins occur in petroleum, they are most diflicult to isolate therefrom. The present invention provides a means of preparing dimethyldecalins from C naphthenes, such as methylcyclopentane or cyclohexane, which are more easily obtained from petroleum.

Tetramethylbenzenes, of which there are three isomers namely, durene, isodurene and prehnitene, are used in various organic syntheses, for example, in the preparation of polycarboxylic aromatic acids. The present invention also provides a means of preparing tetramethylcyclohexanes which can be converted to tetramethylbenzenes by dehydrogenation.

According to one embodiment of this invention, a C naphthene or a mixture of such naphthenes is contacted at a temperature in the range of -20 C. to 80 C., preferably 20 C. to 75 C., with a preformed liquid catalyst complex obtained by reacting a paraflin hydrocarbon having at least eight carbon atoms per molecule with AlCl HCl or AlBr HBr. Under these conditions the naphthene dimerizes to form a C naphthene which isomerizes to an equilibrium mixture of dimethyldecalins. This reaction involves the abstraction of a hydrogen atom from each C naphthene molecule. The hydrogen reacts with the catalyst complex and slowly causes it to disappear. As a result of this reaction AlCl or AlBr is released from the complex and dissolves in the hydrocarbon phase, while HCl or HBr is simultaneously evolved as a gas from the complex.

According to a second embodiment of the invention,

Patented Oct. 10, 1967 ice in either embodiment of the invention. Examples are cyclohexane, methylcyclopentane, dimethylcyclobutane, ethylcyclobutane or mixtures thereof. Under the reaction conditions the C naphthene will readily equilibrate to an equilibrium mixture of C naphthenes of which cyclm hexane predominates but which also contains a substantial amount of methylcyclopentane. The methylcyclopentane will undergo dimerization to C naphthenes which isomerize to an equilibrium mixture of dimethyldecalins. As the methylcyclopentane is consumed more is formed from the cyclohexane by equilibration.

In the second embodiment of this invention, a mixture of any C naphthene and any paraffin hydrocarbon material having seven or more carbon atoms per molecule can be employed as the starting material. The parafiin used can be any heptane, octane, nonane or higher molecular weight paraflin, for example, parafiin wax or mixtures of such parafiins. An isooctane or a mixture of isooctanes is the preferred paraflin charge component.

In preparing the liquid complex used as catalyst in the present system any paraflin hydrocarbon or mixture of such paraflins having eight or more carbon atoms can be used, but it is desirable to use a branched parafiin, e.g., one having at least two brances, in order to reduce the time for preparing the complex.

Preparation of the catalyst complex comprises dissolving or suspending AlCl or AlBr in the parafiin hydrocarbon and passing HCl or HBr into the mixture. This dimethyldecalins and tetramethylcyclohexanes can be prepared simultaneously by reacting, under certain conditions hereinafter specified, one 'or more parafiin hydrocarbons having at least seven-carbon atoms per molecule with a C naphthene.

In my copending application, Ser. No. 39,824, I

filed June 30, 1960, now U.S. Patent No. 3,103,540 a process has been described and claimed for making tetramethylcyclohexanes from a C naphthene and a paraflin hydrocarbon having seven or more carbon atoms, which reactants are the same as used in the second-mentioned embodiment of the present process. In the process of said application the reaction system is homogeneous, with the catalyst, which is a combination of AlBr and HBr, being dissolved in the hydrocarbon reactants; and in order to avoid undesirable cracking reactions, there must be I present in the reaction mixture from 5% to 35% by Weight, based on the total hydrocarbon present, of a C C naphthene, and also the reaction must be carried out in the presence of hydrogen at a partial pressure of 25-500 p.s.i. In such reaction substantially no dimethyldecalins are produced; In the second-mentioned embodiment of the present process different reaction conditions are employed and substantial amounts of dimethyldecalins are produced in addition to the tetramethylcyclohexanes.

Any C naphthene is suitable for use as a charge stock can be done at room temperature, although the use of an elevated temperature may be desirable to increase the rate of reaction. For best results at least five moles of the paraffin per mole of AlCl or AlBr should be employed. Under these conditions some of the parafiin apparently breaks'into fragments, yielding a C fragment which becomes the hydrocarbon portion of the complex. As the reaction proceeds the mixture becomes milky and the yellow liquid complex then precipitates from the hydrocarbon phase. Addition of HCl or HBr is continued until .the milky appearance has disappeared. For obtaining the most active catalyst complex the addition of HCl or HBr should be stopped at this point. The resulting complex is a stable colored liquid having high catalytic activity at temperatures as low as -20 C.

The preformed catalyst complex used in this invention vis to be distinguished from other Friedel-Crafts catalyst the instant system hydrogen halide is evolved as a gas as contrasted with the so-called conventional system in which a hydrogen halide is generally constantly added in an attempt to counteract the depletion reaction of the aluminum halide with the hydrocarbon.

The catalyst complex can be used in the reaction mixture in widely varying proportions, for example, from 5% to 500% by weight based on the hydrocarbon. The larger the'amount of catalyst used the faster will be the reaction rate and of course the less often will additional complex have to be added to make up for that which is lost by physical means.

As previously indicated the present process can be employed to form a mixture of tetramethylcyclohexanes and dimethyldecalins and furthermore can be adjusted to favor the formation of either tetramethylcyclohexanes or dimethyldecalins.- Formation of the dimethyldecalins is favored by the use of 'arelatively high ratio'of the Ci,

naphthene to the charge paraflin and a relatively high reaction temperature, while lower C naphthene to parafiin ratios and lower reaction temperatures are favorable for the formation of tetrarnethylcyclohexanes. In order to cause the latter to predominate in the reaction product, it is desirable to employ a C naphthene to parafiin ratio in the range of 2:1 to 0.5 :1 and a temperature less than about 45 C. For the dimethyldecalins to predominate over the tetramethylcyclohexanes, it is desirable to have a C naphthene to parafiin ratio in the reaction mixture within the range of 100:1 to 10:1 and to use a temperature of 35-60 C.

It has been stated above that the instant invention is to be conducted at a temperature in the range of from about 20 C. to about 80 C., preferably from about 20 C. to 75 C. It is important to the success of the instant invention that the reaction temperature not be allowed to exceed about 80 C. If this temperature is exceeded the naphthene becomes converted to an olefin and dissolves in the catalyst complex and becomes unavailable as a further reactant.

In accordance with the second embodiment of this invention wherein a C naphthene is reacted with a parafiin hydrocarbon it is important to the success of this invention that the paraffinic hydrocarbon contain at least seven carbon atoms. When paraflins having sixor less carbon atoms are used, no substantial yields of tetramethylcyclohexanes are obtainable.

The following examples illustrate the invention more specifically:

EXAMPLE I Preparation of dimethyldecalins by dimerization of methylcyclopentane A catalyst complex was prepared by admixing g. of AlB r with 8 ml. of dimethylhexanes and then bubbling in HBr until no further absorption thereof was obtained. The complex separated from the excess dimethylhexanes as a yellow oily layer which contained about 1 g. of H-Br, and the excess hydrocarbon was removed. A reaction mixture was prepared in a small glass reactor, the mixture being composed of 6.0 g. of the complex and 5.0 ml. of methylcyclopentane. The mixture was continuously shaken on a rocker arm and reacted at a temperature of 27 C. At times of 65, 195 and 320 minutes, small samples of the hydrocarbon phase were taken and analyzed for hydrocarbon composition by vapor phase chromatography. After the last-mentioned sampling the reaction temperature was raised to 51 C. and the reaction was conducted for 60 minutes more, after which a sample of the hydrocarbon phase was tested. Results are shown in Table I.

TABLE I Reaction Time (minutes) Product Composition (wt. percent) 04 paraifins O5 paladins Ca parafiins Methylcyclopentan Cyclohexane C1 naphthenes. Cg naphthenes C naphtheues C10 naphthenes. Methyldecalins Dimethyldecalinso mmoowmqoommoaq an E PPPFFS PPPE" oarqasoooocawoxm 4 EXAMPLE II Preparation of dimethyldecalins by dimerization of methylcyclapentane This example was carried out in the same manner as the preceding example except that in this case the reaction temperature was about 60.8 C. throughout the run. Results are shown in Table II.

TABLE II J Reaction Time (minutes) Product Composition (wt. percent) C4 paraffins. 1.0 1. 5 2. 7 C paraifins. 0. 4 0.6 0.7 C parafiins 0.9 1.4 2.4 Methylcyclopentane 17. 6 16. 8 15. 7 Cyclohexane 68. 8 65. 1 60. 0 C1 naphthenes 1.0 1. 2 1. 5 C5 naphthenes... 1.1 1. 4 2. 3 C9 naphthenes 0. 5 0.7 1. 0 C10 naphthenes 0. 5 0.6 1.0 Dec in Trace Trace Trace Methyldecalin Trace 0. 1 0. 2 Dimethyldecalin 8. 2 10. 5 12. 4

EXAMPLE III Preparation of mixture of dimethyldecalins and tetramethylcyclohexane This example was carried out in a similar manner as the preceding example except that in this case the charge mixture contained 4.5 ml. of methylcyclopentane and 0.5 ml. of n-octane, corresponding to a volume ratio of C naphthene to parafiin of 9:1. Results are shown in Table III.

TABLE III Reaction time (minutes) Product composition (wt. percent) C4 parafiins C parafiins Ca paratfins Met hylcyclopentane Cyclohexane- C7 naphthenes. C naphthenes- Cg naphthenes Cmnannthenos Methyldpoalins Dimethyldecalins In this case the C naphthenes (mainly tetramethylcyclohexanes) and dimethyldecalins were formed in approximately equal amounts. The yield of C naphthenes, based on the amount of the two hydrocarbon reactants consumed, was about 30% and that of the dimethyldecalins, based on the C naphthene consumed, was about 44%.

EXAMPLE IV Preparation of mixture of dimethyldecalins and tetramethylcyclohexane in which tetramethylcyclohexane predominates A catalyst complex was prepared as stated in Example I. A reaction mixture was prepared in a small glass reactor, the mixture being composed of 6.0 g. of the complex, 2.0 ml. of methylcyclopentane and 2.0 ml. of n-octane. The mixture was continuously shaken on a rocker arm It is shown in Table V that even after 276 minutes,

in reaction mixture A, there was produced a total of only 1.4% C naphthenes which were mainly tetramethyl- TABLE V Mixture Reaction Time, minutes 98 276 60 371 59 227 Amount C naphthene in product 0.8 1. 4 0.8 1. 7 8.3 9. 2 Amount dimethyldecalin in product 2. 2 3. 7 1. s 4. 7 2.8 4. 3

cyclohexanes and 3 .7 dimethyldecalins. After 371 by vapor phase chromatography. Results are shown in Table IV.

TABLE IV Reaction time (minutes) Product composition (wt. percent) C4 paraflins 13. 7 21. 7 25. 3 C paratfins 2. 5 4.0 4. 5 Ct paraflins 0.7 1.1 1. 4 Methylcyclopentane 4. 6 4. 3 2. 2 Cyclohexane 25.1 25. 5 22. 1 Doubly branched octanes 3. 8 1. 3 Singly branched octanes- 8. 3 2. 8 1.9 Normal octane 3. 3 C naphthenes 0.9 1.5 1.9 09 naphthenes 1. 6 2. 6 3.2 Cw naphthenes. 23.0 30. 6 31.0 Methyldecalins Trace 0. 2 0. 5 Dimethyldeca1ins 2. 5 4. 3 6. 0

The tabulated data show that both C naphthenes and dimethyldecalins were formed, with the C naphthenes predominating. The C naphthenes were mainly tetramethylcyclohexanes. From the data it can be calculated that about 74% of the two hydrocarbon reactants were consumed in 319 minutes and that about 42% by weight of the amount consumed was converted to C naphthenes. Also it can be calculated that about 23% of the C naphthenes consumed was dimerized to dimethyldecalins. The C -C paraffins formed were mainly isoparaflins. The data indicate that a substantial amount of isobutane was formed. It may be noted that the unconsumed C naphthene had isomerized largely to cyclohexane.

The following example demonstrates why it is necessary in the reaction between a C naphthene and a paraffinic hydrocarbon that the paraffinic hydrocarbon contain at least seven carbon atoms.

EXAMPLE V A catalyst complex as set forth in Example I was used. Three diflerent reaction mixtures were prepared in small glass reactors. The first mixture (designated A) was composed of 6.0 g. of the complex, 2.5 ml. of methylcyclopentane and 2.5 ml. of n-pentane. The second reaction mixture (designated B) was composed of 6.0 g. of complex, 2.5 ml. of methylcyclopentane and 2.5 ml. of 3- methylpentane. The third reaction mixture (designated C) was composed of 6.0 g. of the complex, 2.5 ml. of methylcyclopentane and 2.5 ml. of 3-rnethylhexane. These mixtures were continuously shaken and reacted at a temperature of about 31 C. Small samples of the hydrocarbon phases were taken periodically and analyzed for hydrocarbon composition by vapor chromatography. Comparative results are shown in Table V.

minutes, in reaction mixture B, there was produced only 1.7% C naphthenes which were primarily tetramethylcyclohexanes and 4.7% dimethyldecalins. It is clearly apparent however that, in reaction mixture C wherein the paraflinic hydrocarbon reactant contained seven carbon atoms, the yield of C naphthene, which was primarily tetramethylcyclohexane, was increased to 9.2% as com-pared with yields of 1.4 and 1.7% in reaction mixtures A and B wherein the parafiinic hydrocarbon reactant was a C and C parafiin respectively. It is also noted that this higher yield in reaction mixture C was obtained in a shorter reaction time annd that the yield of C naphthene was not obtained at the expense of the dimethyldecalins since the yield of dimethyldecalins did not substantially decrease from that shown in reaction mixture B.

When any other C naphthene is substituted for methylcyclopentane and when AlCl -HCl is substituted for AlBr -HBr, essentially equivalent results are obtained as those shown in the preceding examples.

I claim:

1. Method for preparing dimethyldecalins which comprises contacting a C naphthene hydrocarbon feed substantially free of parafiin hydrocarbon of seven or more carbon atoms at a temperature in the range of 20 C. to 80 C. with a preformed liquid catalyst complex obtained by reacting a paraifin hydrocarbon having at least eight carbon atoms with an aluminum halide selected from the group consisting of AlCl and AlBr and a hydrogen halide selected from the group consisting of HCl and HBr.

2. Method according to claim 1 wherein the temperature is in the range of 20 C. to C.

3. Method in accordance with claim 2 wherein the preformed liquid catalyst complex is obtained by reacting AlBr -HBr and a paraffin hydrocarbon having at least eight carbon atoms.

4. Method in accordance with claim 2 wherein the preformed liquid catalyst complex is obtained by reacting AlCl -HCl and a paraffin hydrocarbon having at least eight carbon atoms.

References Cited UNITED STATES PATENTS 2,396,331 3/1946 Marschner 260-666 2,398,563 4/1946 Smith et a1. 260-683.77 2,415,066 1/1947 Ross et al. 260-666 3,104,266 9/1963 Kron 260-666 DELBERT E. GANTZ, Primary Examiner.

DANIEL E. WYMAN, PATRICK P. GARVIN, AL-

PHONSO D. SULLIVAN, Examiners.

0 C. E. SPRESSER, Assistant Examiner. 

1. METHOD FOR PREPARING DIMETHYLDECALINS WHICH COMPRISES CONTACTING A C6 NAPHTHENE HYDROCARBON FEED SUBSTANTIALLY FREE OF PARAFFIN HYDROCARBON OF SEVEN OR MORE CARBON ATOMS AT A TEMPERATURE IN THE RANGE OF -20*C. TO 80*C. WITH A PREFORMED LIQUID CATALYST COMPLEX OBTAINED BY REACTING A PARAFFIN HYDROCARBON HAVING AT LEAST EIGHT CARBON ATOMS WITH AN ALUMINUM HALIDE SELECTED FROM THE GROUP CONSISTING OF ALCL3 AND ALBR3 AND A HYDROGEN HALIDE SELECTED FROM THE GROUP CONSISTING OF HCL AND HBR. 